Incorporation of Al2O3 and ZrO2 ceramics to AZ31 magnesium alloys composite coating using micro-arc oxidation method.

In this research, a composite coating with Al2O3 and ZrO2 particles have been applied on AZ31 magnesium alloy by micro-arc oxidation (MAO) technique. The alkaline electrolyte included a constant based composition and different composition of the Al2O3 and ZrO2 additives. Microstructure observations reveal that the surface pores of composite coating reduced during addition of ZrO2 and Al2O3 ceramic particles. The hardness of coating increased from about 380 for non-added to 620 MPa for Al2O3+ZrO2 added coating and wear rate reduced about 8 times. Wettability of the coating increased by incorporation of Al2O3 and/or ZrO2 particles while, Al2O3 is more effective than ZrO2. Addition of the ceramic particles enhanced the hydrophilicity properties of surface in wettability test and a contact angle of 43° was obtained for coating including Al2O3+ZrO2. The antibacterial properties of MAO coatings showed that S. aureus bacterium is more sensitive to the zirconia and alumina particle than S. typhimurium bacterium after 24 h of incubation.

Association of aplastic anaemia and Fanconi's disease with HLA-DRB1 alleles.

One of the most fascinating areas of research within the field of histocompatibility at present time concerns an observation that a major human histocompatibility system, human leucocyte antigen (HLA), is deeply involved in the development of a great number of diseases. Major histocompatibility complex is the most polymorphic system in the genome of different species. Recognition of HLA alleles could be useful in transplantation and disease studies. Genetic construct of HLA DRB1 was studied in Iranian normal populations and patients with aplastic anaemia and Fanconi's disease. DNA was extracted from the whole blood of 466 normal, 35 aplastic anaemia and 10 Fanconi's individuals. Then DRB1 gene polymorphism was studied by polymerase chain reaction-sequence-specific primer method. The HLA DRB1 gene analysis showed increase of DRB1*07 in aplastic anaemia patients compared to normal population (P = 0.02). According to this study, the frequency of DRB1*07 in normal individuals was 8.3, and in aplastic anaemia patients, 15.7%. Additionally, the frequency of DRB1*04 in normal, aplastic anaemia and Fanconi's individuals was 10, 5.7 and 20%, respectively. Our results of investigation showed correlation between some HLA alleles with the studied diseases. We reported the frequency of various DR types in aplastic and Fanconi's patients. This study could imply the possible role of HLA-DRB1*07 in the incidence of aplastic anaemia. Moreover, the frequency of DRB1*04, DRB1*03 and DRB1*15 alleles showed intermediate correlation with Fanconi's anaemia.

Heterozygous familial hypercholesterolemia: failure of normal allele to compensate for mutant allele at a regulated genetic locus.

In normal human fibroblasts, the synthesis of a cell surface receptor for plasma low density lipoprotein (LDL) is regulated by a sensitive system of feedback suppression. The number of functional LDL receptors declines by more than 20 fold when cellular stores of esterified cholesterol are increased by incubation of cells with an exogenous source of cholesterol. Fibroblasts from patients with the heterozygous form of familial hypercholesterolemia (FH) possess one functional allele and one nonfunctional allele at the LDL receptor locus. In the current studies, we have examined the effect that this deficiency produces upon the pattern of regulation of the single functional allele at the LDL receptor locus. Under growth conditions that induced a maximal rate of LDL receptor synthesis (that is, growth in the absence of an exogenous source of cholesterol), the FH heterozygote cells produced about one half as many functional LDL receptors as did the normal cells. More importantly, when grown in the presence of increasing amounts of exogenous cholesterol, the FH heterozygote and normal cells suppressed their respective LDL receptor activities in parallel. Over a wide range of LDL receptor activities, at each level of cellular esterified cholesterol, the FH heterozygote cells expressed about one half as many receptors as did the normal cells. These data indicate that in the FH heterozygote cells, the receptor regulatory mechanism dictates that the normal allele produce only the amount of gene product that it would normally produce at a given level of cellular esterified cholesterol. The failure of the regulatory mechanism to stimulate the normal allele at the LDL receptor locus to produce twice its normal amount of gene product leaves the FH heterozygote cells with a persistent 50% deficiency in LDL receptors under all conditions of cell growth.

Restoration of a regulatory response to low density lipoprotein in acid lipase-deficient human fibroblasts.

Previous studies have shown that cultured fibroblasts derived from patients with genetic defects in lysosomal acid lipase (i. e. the Wolman Syndrome and Cholesteryl Ester Storage Disease) are defective in their ability to hydrolyze the cholesteryl esters contained in plasma low density lipoprotein (LDL). As a result, these mutant cells show a reduced responsiveness to the regulatory actions of LDL, as evidenced by a decreased LDL-mediated suppression of the activity of 3-hydroxy-3-methylglutaryl coenzyme A reductase and by a decreased LDL-mediated activation of cellular cholesteryl ester formation. In the current studies, the Wolman Syndrome and Cholesteryl Ester Storage Disease cells were grown in the same Petri dish with mutant fibroblasts derived from a patient with the homozygous form of Familial Hypercholesterolemia. Whereas pure monolayers of either the Familial Hypercholesterolemia cells (lacking cell surface LDL receptors) or the acid lipase-deficient cells (lacking cholesteryl ester hydrolase activity) responded poorly to LDL, the mixed monolayers developed lipoprotein responsiveness as measured by an enhancement of both LDL-mediated suppression of 3-hydroxy-3-methylglutaryl coenzyme A reductase activity and LDL-mediated stimulation of cholesteryl ester formation. This effect was shown to result from the release of the lysosomal acid lipase from the Familial Hypercholesterolemia homozygote cells into the culture medium and its subsequent uptake by the acid lipase-deficient cells. The acquisition of this acid lipase activity enhanced the ability of the Wolman Syndrome and Cholesteryl Ester Storage Disease cells to respond to the lipoprotein by suppression of 3-hydroxy-3-methylglutaryl coenzyme A reductase and activation of cellular cholesteryl ester formation. These data emphasize the importance of the lysosomal acid lipase in the cellular metabolism of LDL cholesteryl esters and, in addition, demonstrate that delivery of this enzyme to genetically deficient cells can enhance the regulatory response to the lipoprotein.